Page 18 - Feline Cardiology

8 Section A: Clinical Entities

Associations between Heart Murmurs and tract stenosis is an important and common cause of
Cardiovascular Disease innocent murmurs in cats (Rishniw and Thomas 2002;
Certain murmurs are pathognomonic for specific dis- Allen et al. 2010). In the authors’ experience, soft (≤
Clinical Entities heart base is almost always caused by a patent ductus that disappear at slower heart rates are more likely to be
grade 4/6), musical quality murmurs at the heart base
eases. For example, a continuous murmur at the left
innocent, particularly if thoracic radiographs reveal a
arteriosus (although rarely an aortic-pulmonary window
normal heart size; however, enough overlap exists with
or an arteriovenous fistula can produce a similar
murmur). A systolic murmur with a point of maximal
definitive conclusion from being reached on ausculta-
intensity at the right heart base is usually associated with mild forms of HCM and other disorders to prevent any
a ventricular septal defect. See Box 1.4 for a list of tion alone. While ausculting the feline patient, it is often
murmur characteristics for the common feline cardiac possible to slow the heart rate by covering the cat’s face
diseases. However, it is often impossible to differentiate in the examiner’s hand or in the crook of the examiner’s
innocent (benign) murmurs from those murmurs sec- arm (Figure 1.2).
ondary to heart disease based on auscultation alone— Changes in heart murmur characteristics are common
particularly in the cat, where innocent murmurs are very when a cat’s heart rate changes. The clinical significance
common. Benign dynamic right ventricular outflow of this phenomenon is mixed: in many instances, a
murmur that appears only during tachycardia can be
benign (e.g., dynamic RVOT outflow obstruction). But
in many other cases such a murmur is associated with
Box 1.4. Murmur characterization based on point of maxi- structural heart disease: a cat with a murmur audible
mal intensity and timing
only when the cat is provoked or aroused is 6.1 times
more likely to have dynamic ventricular outflow tract
Left heart base
Systolic obstruction than a cat that does not develop a murmur
Aortic stenosis (dynamic or fixed; including hypertrophic under the same circumstances (Paige et al. 2009).
obstructive cardiomyopathy) Therefore, the appearance of a heart murmur, or an
Pulmonic stenosis (dynamic or fixed) increase in murmur intensity, when the heart rate
Tetralogy of Fallot increases is not a finding that definitively confirms either
Physiologic (benign) a benign or a pathologic condition. It is also important
Continuous to remember that it is possible to create murmurs, par-
Patent ductus arteriosus ticularly in lean small animal patients, by applying
Diastolic (rare) excessive pressure to the cat’s thorax with the stetho-
Aortic regurgitation
scope chest piece/head. When a murmur is ausculted, it
Left heart apex is useful to reduce the pressure with which the stetho-
Systolic
Mitral regurgitation
Physiologic (benign)
Diastolic (rare)
Mitral stenosis

Parasternal
Systolic
Left ventricular outflow tract obstruction (dynamic or
fixed; including hypertrophic obstructive cardiomyopa-
thy)
Dynamic right ventricular outflow tract obstruction
Ventricular septal defect
Physiologic
Right heart base
Systolic
Ventricular septal defect (left to right)
Dynamic right ventricular outflow tract obstruction Figure 1.2. During auscultation, gently covering the feline pa-
tient’s face with the hand or in the crook of the arm often results
Right heart apex
Systolic in appreciable slowing of the heart rate. This technique is useful
Tricuspid regurgitation to aid in accurately determining the timing of heart sounds, as
well as to see whether the murmur character changes.